Johne's disease has been reported in almost all countries around the world. Johne's disease or paratuberculosis, is a chronic wasting disease that causes considerable production losses in adult cattle, sheep, goats, deer, llamas, elk, bison, and other ruminants. The disease is caused by Mycobacterium paratuberculosis, a bacterium related to tuberculosis.
Johne's disease typically starts as an infection in calves, though visible signs do not generally appear until cattle are 2 to 5 years of age (and sometimes much older). The infection is difficult to detect in its early stages. This bacterium causes an inflamed intestinal tract, results in severe weight loss, diarrhea and lower milk production. Infected cattle frequently eat well, and look bright, however, they appear to be unthrifty. Body temperature may be or may not be elevated. There is no cure for Johne's disease once an animal becomes infected.
Eradication of Johne's disease is extremely difficult because of its insidious nature, long incubation period, difficulty in early detection, and major management changes necessary to prevent and eradicate it. Consultation and action by a veterinarian experienced in the management of Johne's disease is necessary for the development of heard-control and eradication program.
The causative agent of Johne's disease is Mycobacterium avium subsp. paratuberculosis, MAP. This infection is found in domestic ruminants (e.g., cattle, sheep and goats and wildlife and is responsible for overwhelming losses in dairy production worldwide. Animals that are afflicted with MAP progress from silent infection to a subclinical phase in which no physical symptoms are present; however, subtle levels of shedding can contaminate the heard during these stages. Once the physical symptoms of weight loss and chronic diarrhea are present at the clinical and advanced cellular disease phases, the damage to the cattle population has already occurred with resulting large financial losses to the farmer and the cattle industry.
Diagnosis of the disease in live individual animals is difficult for a number of reasons. To date, “there is no single, good test for paratuberculosis. As a result a combination of tests is often used.” It seems that it is easier to diagnosis the presence in a herd as opposed to individual animals. Most of the time, the definitive diagnosis is done after an animal has died. There is current research occurring to attempt to develop better diagnostic methods for this difficult disease.
To control the spread of this disease, a detection method must be rapid, field worthy, cost effective, sensitive to low levels of shedding, and selective for MAP over other commonly occurring bacteria. Currently available methods tend to fall short of these goals as bacteriologic culturing methods are lengthy (12-16 weeks); serological tests suffer from a lack of sensitivity at subclinical levels; and gamma interferon and nucleic acid probe tests have low specificity.
In view of the shortfall of bacteriologic culture methods, serologic tests, interferon and nucleic acid probe tests, there is a continuing need for a simple field worthy test that can be inexpensively run and quickly run to improve upon current techniques for early detection of Johne's disease. This invention has the development of such a test as its primary objective.